Environmental Survey Using Electrical Conductivity and the Global Positioning System in a Wetland

Abstract

We conducted an environmental survey of a wetland using electrical conductivity (EC) measurement and the global positioning system (GPS) in the flood plain of Furen river (43° 17′ N, 145° 15′ E). We used a new portable instrument developed by Kawauchi et al. that can measure apparent EC of different depths. Two electrodes at different intervals (20 and 40 cm) were used to collect data from depths of 20-40 cm. In order to determine the latitude and longitude of measurement sites, differential global positional (DGPS) correction signals within 200 km of a differential beacon operated by the Japan Coast Guard were used. Kushirozaki radio station (42° 58′ N, 144° 23′ E) was used in this survey. We hiked in the wetland carrying an aluminum backpack frame to which a GPS receiver, a DGPS receiver, a mobile computer and a 12-volt battery with a satellite antenna and a 300-kHz DGPS whip antenna were attached and holding a stick to which an earth cable was attached.
We were able to receive strong DGPS correction signals while sounding the survey. In stationary GPS measurements with DGPS corrections and a good view of the sky, error decreased within an average radius of only 2. 5m due to the lack of the big trees in wetland and due to the cancel on May 2, 2000 of the noise signal (S/A) by the U. S. government. Using our system, we were able to survey an area of 2 km EW x 0. 7 km NS within 2 days. From these measurements, we were able to determine the EC distribution in horizontal and vertical directions of the survey area. EC in the area near the pasture and Furen river was higher than that in the area between them and was highest in the border area of the pasture and river. Most of the trees in the wetland were growing in the areas in which EC was high, mainly near the pasture and road. EC at a depth of 40 cm was higher overall than that at a depth of 20 cm.